1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and a method for fabricating an LCD device, and more particularly, to a multi-domain liquid crystal display (LCD) device and a method for fabricating an LCD device.
2. Discussion of the Related Art
As demand for various types of display devices increases various flat display devices, such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, electroluminescent display (ELD) devices, and vacuum fluorescent display (VFD) devices, are being developed. Some of the flat display devices are commonly used due to characteristics of thin profile, light weight, and low power consumption, thereby substituting cathode ray-tube (CRT) devices with the LCD devices. In addition, mobile type LCD devices, such as displays for notebook computers, are being developed, and LCD devices were developed for computer monitors and televisions.
Despite various technical developments within the LCD device technology, enhancement of picture quality of the LCD device has been lacking. Thus, in order to use the LCD devices as general display devices, the development of LCD devices having high image quality, such as high resolution and luminance, with large-sized screens is necessary while still maintaining light weight, thin profile, and low power consumption. Currently, multi-domain LCD devices having at least two different alignment directions within one pixel region have been developed to obtain LCD devices having wide viewing angles.
FIG. 1 is a schematic perspective view of an LCD device according to the related art. In FIG. 1, an LCD device includes first and second substrates 1 and 2, and a liquid crystal layer 3 formed by injecting liquid crystal between the first and second substrates 1 and 2. More specifically, the first substrate 1 includes a plurality of gate lines 4 arranged along a first direction at fixed intervals, a plurality of data lines 5 arranged along a second direction perpendicular with the gate lines at fixed intervals to define a plurality of pixel regions P, a plurality of pixel electrodes 6 each within the pixel regions defined by the plurality of gate and data lines, and a plurality of thin film transistors (TFTs) T being turned ON and OFF according to driving signals transmitted along the gate lines 4 for passing video signals transmitted along the data lines to the pixel electrodes 6.
The second substrate includes a black matrix layer 7 for preventing light leakage within regions, except the pixel regions of the first substrate, and R/G/B color filter layers for producing colored light, and a common electrode 9. Although not shown, alignment layers are formed on opposing surfaces of the first and second substrates 1 and 2 to align liquid crystal molecules of the liquid crystal layer 3 by a rubbing method. Accordingly, the thin film transistor T includes a gate electrode that protrudes from the gate line 4, a gate insulating layer formed along an entire surface of the first substrate 1, a source electrode that protrudes from the data line 5, and a drain electrode opposing the source electrode.
The pixel electrode 6 is formed of transparent conductive metal having a high transmittance of light, such as indium-tin-oxide (ITO), and the liquid crystal layer 3 is formed of Twisted Nematic (TN) mode liquid crystal material, wherein the light oscillating along a longitudinal direction of the liquid crystal molecules has a first refractive index different from a second refractive index of the light oscillating along a direction vertical to the longitudinal direction of the liquid crystal molecules, thereby creating narrow viewing angles. Accordingly, instead of using the TN mode liquid crystal material, the liquid crystal layer is formed of Vertical Alignment (VA) mode liquid crystal material, whereby the liquid crystal molecules are aligned along different directions by distorting an electric field.
FIG. 2 is a cross sectional view of a unit pixel for a multi-domain LCD device according to the related art. In FIG. 2, upper and lower substrates 70 and 80 are formed to oppose each other, and a liquid crystal layer 90 is formed between the upper and lower substrates 70 and 80. In addition, projections 60 are formed along inner facing surfaces of the upper and lower substrates 70 and 80, wherein one projection 60 is formed at a center position of the inner surface of the upper substrate 70, and the other projections 60 are formed on the left and right sides of the inner surface of the lower substrate 80. If the projection 60 is formed of a material having a dielectric constant lower than a dielectric constant of the liquid crystal molecule 92, the electric field 94 (arrow direction) is formed outward to the projection 60 of the upper substrate 70. In addition, the liquid crystal molecules 92 are aligned in perpendicular to the electric field 94, whereby the arrangement of the liquid crystal molecules is divided into first and second domains A and B. Thus, distortion of the electric field is attenuated as the difference of the dielectric constant between the projection 60 and the liquid crystal molecule 92 increases. Accordingly, as the projections 60 are formed of material having a dielectric constant greater than a dielectric constant of the liquid crystal molecule 92, it is possible to obtain a stable multi-domain LCD device.
However, the related art multi-domain LCD device has the following disadvantages. In the related art multi-domain LCD device, the distortion of the electric field is formed by the projections formed on the inner surfaces of the lower and upper substrates. As a result, the aperture ratio lowers by the occupying area of the projections on the inner surfaces of the lower and upper substrates, thereby lowering the luminance. However, since the multi-domain LCD device requires rubbing fixation or electrode structures to determine the alignment direction of the liquid crystal molecules, complicated manufacturing processes are required that increase manufacturing costs.